Multiple die stack apparatus employing T-shaped interposer elements

ABSTRACT

Multiple integrated circuit devices in a stacked configuration that use a spacing element for allowing increased device density and increased thermal conduction or heat removal for semiconductor devices and the methods for the stacking thereof are disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/933,843,filed Sep. 2, 2004, now U.S. Pat. No. 7,064,006, issued Jun. 20, 2006,which is a divisional of application Ser. No. 09/989,326, filed Nov. 20,2001, now U.S. Pat. No. 6,911,723, issued Jun. 28, 2005, which is acontinuation of application Ser. No. 09/247,009, filed Feb. 8, 1999, nowU.S. Pat. No. 6,351,028, issued Feb. 26, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the packaging of integratedcircuit devices by interposing a plurality of integrated circuit deviceswithin a common package for increased semiconductor device density. Moreparticularly, the present invention relates to multiple integratedcircuit devices in a stacked configuration that uses a spacing elementallowing increased semiconductor device density and allowing betterthermal conductivity for dissipating heat for semiconductor memorydevices, semiconductor processor type devices, or any desired typeintegrated circuit semiconductor device.

2. State of the Art

Integrated circuit semiconductor devices have been known since shortlyafter the development of the electronic transistor device. The goals indesigning and manufacturing semiconductor devices have been to make thedevices smaller, more complex, with higher densities, and to includeadditional features. One method that improves the features and thedensities of the semiconductor devices is to shrink the line sizes usedin the lithographic process step in fabricating semiconductor devices.For example, each one-half reduction in line width of the circuits ofthe semiconductor device corresponds to a four-fold increase in chipdensity for the same size device. Unfortunately, increasing densitysimply through improved lithographic techniques is limited because ofphysical limits and the cost factor of scaling down the dimensions ofthe semiconductor device. Accordingly, alternative solutions to increasesemiconductor device density have been pursued. One such alternative hasbeen the stacking of multiple semiconductor devices. However,conventional stacking of semiconductor devices can lead to excessivelocal heating of the stacked semiconductor devices as well as lead torestraints on how the heat may be removed from the stacked semiconductordevices.

One approach of semiconductor device (die) stacking uses a chip geometryknown as cubic chip design and is illustrated in drawing FIG. 1 (PriorArt). The device 2 includes substrate 4, upon which a plurality ofsemiconductor devices 6 is stacked. Each semiconductor device 6 isconnected to another semiconductor device and to substrate 4 via bondingelements 8, which are then encased in a suitable type of resin material10 forming a package. The semiconductor devices 6 are designed such thatan overhanging flange is provided by cutting the edges of asemiconductor device at approximately a 30- to 35-degree angle andinverting the device for the bonding connection. This allows thesemiconductor devices 6 to stack one on top of another in a uniform andtight arrangement.

Unfortunately, the cubic design has several disadvantages that make itunsuitable for all types of semiconductor device packaging design. Onedisadvantage is that the cubic stacking of the semiconductor devices oneon top of another causes stack stresses or bending, or both.Additionally, because of stack stressing or bending, there is a limit tothe number of semiconductor devices that can be stacked one on top ofanother. Also, if the adhesive of the stack weakens and comes loose, thesemiconductor device will shift, which can result in the breaking of thebonds between the various devices 6 and the substrate 4. Furthermore,the stacking of the semiconductor devices generates thermal andmechanical problems where the semiconductor devices generate beat thatcannot be easily dissipated when they are stacked one upon another.

Additional solutions have been developed in the prior art and areillustrated in U.S. Pat. No. 5,585,675 ('675 patent) and U.S. Pat. No.5,434,745 ('745 patent). The '675 patent discloses a packaging assemblyfor a plurality of semiconductor devices that provides for stacking ofthe semiconductor devices. The packaging assembly uses angularly offsetpad-to-pad via structures that are configured to allow three-dimensionalstacking of the semiconductor devices. The electrical connection isprovided to a via structure where multiple identical tubes are providedin which a semiconductor device is mounted and then one tube is mountedon top of another tube. The angularly offset via pads are providedthrough the stack tube structure for connection. One disadvantage withthe angularly offset pad via structure is that the tubes must beprecisely manufactured so that the vias are lined up properly. Further,the semiconductor devices must be set within strict tolerances for thetubes to stack one on top of another so the vias can be aligned properlyas well.

The '745 patent discloses a stacked semiconductor device carrierassembly and a method for packaging interconnecting semiconductordevices. The carriers are constructed from a metal substrate onto whichthe semiconductor device attaches. Next, the semiconductor device iswired bonded to the conductor pattern on the substrate and eachconductor is routed to the edge of the substrate where it is connectedto a half circle of a metallized through-hole. Again, the '745 patentdiscloses a tube-like design with half circle vias for allowinginterconnection to the stack of multiple semiconductor devices.

One disadvantage with the stack type semiconductor device carrier of the'745 patent in that the tubes are connected one with another. Anypotential rework operation involving the wire connections is verydifficult in that the tube assemblies must be disassembled for such arework operation.

Accordingly, a multiple stacked arrangement of semiconductor devices andassociated methods of stacking that reduce stack stresses or bending ofthe semiconductor devices, that allow easier reworking of the wiringinterconnecting bond pads of the semiconductor devices, that protect thebond pads of each semiconductor device from the other devices, and thateffectively remove heat from the semiconductor devices are needed.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to the packaging of integrated circuitdevices by interposing a plurality of integrated circuit devices withina common package for increased semiconductor device density. The presentinvention relates to multiple integrated circuit devices in a stackedconfiguration that uses a spacing element for allowing increased devicedensity and the removal of thermal energy from semiconductor devices andthe methods for the stacking thereof.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a prior art cubic semiconductordevice package;

FIG. 2 is a cross-sectional diagram of an embodiment of the T-interposerdevices of the present invention used for the stacking of multiplesemiconductor devices according to the present invention;

FIG. 3 is a perspective view of an embodiment of a single T-interposerof the present invention;

FIG. 4 is a cross-sectional view of multiple semiconductor devicesmounted to an embodiment of a T-interposer according to the presentinvention;

FIG. 5 is a cross-sectional diagram of another embodiment ofT-interposers having differing dimensions of the present invention;

FIG. 6 is a perspective view of an embodiment of an invertedT-interposer of the present invention;

FIG. 7 is a cross-sectional view of a multiple semiconductor device(die) package that has a sealant about the interconnections;

FIG. 8 is a cross-sectional view of another embodiment of theT-interposer of the present invention in a stacked configuration;

FIG. 9 is a cross-sectional view of another embodiment of theT-interposer of the present invention in a stacked configuration; and

FIG. 10 is a block diagram of an electronic system incorporating thesemiconductor device of FIG. 2 and the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Illustrated in a cross-sectional diagram in drawing FIG. 2 is amulti-stacked semiconductor device structure utilizing a T-interposerdevice having a T-shape in cross-section of the present invention.Multiple stack unit 20 comprises a substrate 22, a first semiconductordevice 24 disposed on substrate 22, a first T-interposer 26 disposed onthe first semiconductor device 24, and multiple semiconductor devices 24disposed on multiple T-interposers 26. Each semiconductor device 24includes a plurality of bond pads 28 thereon. Each T-interposer 26includes a substantially vertical stem 27 having substantially verticaledges and T-bar cross portions or members 29 having substantiallyhorizontal edges or surfaces with respect to the vertical edges of thestem 27, the upper surface 29′ of the T-bar members 29 extending acrossthe stem 27 to form a substantially horizontal surface with respect tothe vertical upon which to mount one or more semiconductor devices, 24.The flange (horizontal) edges or surfaces of each T-interposer 26 areoffset so that a portion of the active surface 25 of each semiconductordevice 24 attaches to the base of the stem 27 of an adjacentT-interposer 26 while bond pads 28 of each semiconductor device 24 areexposed for wire bonding to substrate 22 or another semiconductor device24 or the circuit of another T-interposer 26. Each semiconductor device24 is subsequently stacked one on top of another in a horizontal planewith a T-interposer 26 disposed between each semiconductor device 24.Each semiconductor device 24 may be bonded either to the T-interposer26, another semiconductor device 24, or to substrate 22 or both. In thisstructure, the T-interposer 26 is placed on an individual semiconductordevice 24 as other semiconductor devices 24 are stacked one on top ofanother, each stacked semiconductor device 24 being located in aseparate substantially horizontal plane. This provides for access andprotection to bond pads 28 of the semiconductor devices 24. TheT-interposer 26 can be made of a variety of materials, including thosematerials having a coefficient of thermal expansion (CTE) matching orsimilar to the semiconductor device(s) 24, such as silicon, ceramic,alloy 42, etc., and having the desired thermal energy (heat transfer orconductivity) characteristics for the transfer of thermal energy or heatfrom semiconductor devices in contact with or around T-interposer 26.Alternately, the material for the T-interposer 26 may be selected forthermal energy insulation effects to prevent thermal energy from beingtransferred from one semiconductor device 24 connected to theT-interposer to another semiconductor device 24 connected to theT-interposer.

This protects the semiconductor devices 24 during the stacking andenables a variety of interconnections to be used between semiconductordevices 24, T-interposers 26, and/or substrates 22. The interconnectionbetween semiconductor devices 24 or T-interposers 26 or substrates 22,or both, uses conductor traces, tape, wire bonding, conductive paste, orconductive adhesives, or any other type of suitable semiconductorinterconnection technique known to one skilled in the art. TheT-interposer 26 allows bond pads 28 of the semiconductor device 24 to beexposed, so no additional rerouting steps are required to reroute a bondpad 28 to the edges. This is advantageous over the prior art structures,such as the cubic design shown in drawing FIG. 1, in that the shell caseor the interconnection requires additional processing in those materialsand additional time. Further, the flanged edges forming the stem 27 ofT-interposer 26 allow direct connection to the bond pads 28 and contactto all four sides of semiconductor devices 24. This allows increasedinterconnect density between a substrate and a plurality ofsemiconductor devices.

In multiple stack unit 20, if desired, the first semiconductor device24, which is mounted to substrate 22, can be a microprocessor while thesecond semiconductor device 24, located above T-interposer 26 mounted tothe first semiconductor device 24 located on the substrate 22, can be asemiconductor memory device, which allows for mixing and matching of thesemiconductor devices such as memory devices and processing devices andcontrol logic devices for a complete, integrated semiconductor devicepackage.

Referring to drawing FIG. 3, further illustrated is an invertedT-interposer 26 as shown in drawing FIG. 2. Again, T-interposer 26 canbe manufactured to match the same CTE of the semiconductor device 24 orthe semiconductor device substrate 22 used for each of semiconductordevices 24, or both. This allows T-interposer 26 to serve as a thermalor heat dissipation device between each semiconductor device 24 whileallowing for greater heat dissipation than would otherwise be possiblewere the semiconductor devices 24 stacked directly upon each other.Further, T-interposer 26 provides electrical insulation between eachsemiconductor device 24 that would not be otherwise possible were thesemiconductor devices to be stacked one upon another such as in theprior art described in drawing FIG. 1. Additionally, the T-interposer 26may be comprised of two different materials to provide both thermalconductivity from one semiconductor device and thermal insulation withrespect to a second semiconductor device. For instance, the stem 27 maybe of a thermally conductive material while the T-bar members 29 areformed of a thermally insulative material; the stem 27 may be joined tothe T-bar member(s) 29 by any suitable means, such as adhesive bonding,etc. The T-interposer 26 of the present invention provides for muchgreater bonding edge relief for different types of connection deviceswith respect to the bond pad 28 location on the active surface 25 of thesemiconductor device 24 than that shown in the prior art deviceillustrated in drawing FIG. 1 and greater insulation capacity for thebond pads 28 of the semiconductor devices 24 with the T-interposer 26 inplace. Finally, a top T-interposer 26 is further provided for cappingthe device to protect and promote heat transfer from the lastsemiconductor device 24 forming the multiple stacked unit 20.

Still referring to the T-interposer 26 illustrated in drawing FIG. 3, anelectrical bonding interconnect element 30 is manufactured intoT-interposer 26 to provide subsequent connection should the bond pads 28on active surface 25 of the semiconductor device 24 be mounted orconnected to the T-shaped interposer 26 for electrical interconnection.

Referring to drawing FIG. 4, illustrated is a cross-section diagram ofmultiple semiconductor devices 38 and 40 being mounted to a singleT-interposer 26. T-interposer 26 is mounted to a substrate 36. Substrate36 includes bond pads/circuits 28 thereon. Semiconductor device 38 canbe a processor type semiconductor device while semiconductor device 40can be a memory type semiconductor device. Semiconductor device 38 andsemiconductor device 40 are interconnected via bond pads 28 and furtherconnected to bond pads or circuits 28 on substrate 36. Additionally, thebonding wire from one bond pad or circuit 28, such as on device 40, canconnect directly to the device structure to which the substrate 36 is tobe permanently mounted. This can be the actual circuit board, such as amother board used in a computer system. Of course, other directconnection options will be readily apparent to one skilled in the art.

Referring to drawing FIG. 5, illustrated is a cross-sectional diagram ofan arrangement of multiple semiconductor devices 24 similar to thatillustrated in drawing FIG. 4. The present invention illustrated indrawing FIG. 5 further adds multiple stacking upon a particularsemiconductor device 24. Multiple T-interposers 26 are provided and areof similar sizes. Additionally, semiconductor device 24 can be directlyconnected to T-interposer 26 below bond pad 28 thereon. In this manner,substrate 36 mounts directly to mother board substrate 22 whereadditional bonding pads 28 are provided in substrates 22 and 36.

Referring to drawing FIG. 6, depicted is an alternative embodimentT-interposer 126 of the present invention, which is similar to theembodiment of the T-interposer 26 illustrated in drawing FIG. 3. Asillustrated in drawing FIG. 6, the T-interposer 126 includes additionalrecessed sections all around. The entire recessed periphery allowssemiconductor devices that have connection pads around the entireperimeter of the device to be exposed for connection. In this manner,greater inter-connectivity is achieved with the ability to connect verydense interconnected circuit devices to other semiconductor devices.Additionally, ball weld spots 128 are provided as well and allow directelectrical and mechanical connection of any subsequent semiconductordevices. The stem 127 of the T-interposer 126 includes T-members 129therearound and substantially horizontal surface 129′ located thereaboveas described hereinbefore with respect to T-interposer 26.

Referring to drawing FIG. 7, illustrated is a cross-sectional view of amultiple stack unit 20 that is completely sealed or packaged. Again, asubstrate 22 is provided upon which a first semiconductor device 24 ismounted with a T-interposer 26 mounted to the first semiconductor device24. A final cap or top T-interposer 26 is further provided on top of theentire stack unit 20. Lastly, an epoxy interconnect 50 is provided forsealing and/or packaging and electrically isolating the bondingperformed between the multiple semiconductor devices 24. If desired, thetop of the unit 20 may include a heat sink 52 of suitable type materialwhich may include one or more fins 54 (shown in dashed lines) foradditional thermal control of the heat from the unit 20.

Referring to drawing FIG. 8, illustrated is another embodiment of theT-interposer 26 of the present invention in a stacked arrangementbetween semiconductor devices 40, which are electrically connected bywires 56 to circuits 58 of the substrate 36. In this embodiment of theT-interposer 26 of the present invention, one T-bar member 29 has agreater length or extends farther than the opposing T-bar member 29 ofthe T-interposer 26 to provide greater bonding edge relief for differenttypes of connection devices with respect to the bond pad location on theactive surface of the semiconductor device 24 than the bonding edgerelief provided by the T-bar member 29 on the other side of theT-interposer 26. In this manner, the T-interposer 26 is not centrallylocated on a portion of the active surface of the semiconductor device40 but, rather, is located off-center on a portion of the active surfaceof the semiconductor device 40. Such a T-interposer 26 allows for theaccommodation of differing sizes and shapes of semiconductor devices 40and bond pad arrangements thereon for interconnection to the circuits 58of substrate 36.

Referring to drawing FIG. 9, illustrated is another embodiment of theT-interposer 26 of the present invention where the T-interposer 26includes a plurality of stems 27 and T-bar members 29 to form the same,each stem 27 located on a portion of the active surface of asemiconductor device 40, which is, in turn, located on a substrate 36having circuits 58 located thereon connected by wires 56 while wires 62electrically connect the semiconductor devices 40 located on surface 29′of the T-interposer 26 to the circuits 60 located thereon. In thismanner, the T-interposer 26 helps to increase the density of thesemiconductor devices 40 located on the substrate 36 while providingthermal control of the heat generated from the semiconductor devices 40located on the substrate 36 and on the surface 29′ of the T-interposer26.

Each T-interposer 26 can be manufactured in various manners; ideally,the T-interposer 26 consists of a unitary element that is milled ormachined from a single piece. The side edges for producing the “T”effect are milled away to preserve the integral strength of the unitarypiece. This design prevents fractures occurring in seams of theT-interposer where the top “T” portion is epoxied to the bottom as aseparate element. If desired, T-interposer 26 can be made from separatepieces, one having a smaller width than the other, if the epoxy oradhesive used to connect the two elements is of sufficient strength toprevent fracturing or separation, or the strain and load placed on theseams were greatly reduced so as to minimize the possibility offracturing.

The use of the T-interposer 26 for stacking bare dies has severaladvantages over prior art solutions. One advantage is that it reducesstack stresses or bending. Further, the T-interposer allows easierreworking of any bond interconnect when necessary. Additionally, asthere are no stress problems inherent in stacking semiconductor devicesupon other devices, as any number of devices can be stacked withT-interposer 26 used in separating device from device, thus allowing forgreater device densities for memory devices and other type semiconductordevices. Also, several types of interconnect methods are possible withthe T-interposer, such as wire bonding, ball bonding, flip-chip bonding,etc. Additional advantages include the bond pads of each semiconductordevice being protected from one another in the device stack. Thermal andmechanical properties are improved because of the use of theT-interposer. The improved thermal and mechanical properties also allowfor increased semiconductor device density for memory chips and SIMMtype devices.

Those skilled in the art will appreciate that semiconductor devicesaccording to the present invention may comprise an integrated circuitdie employed for storing or processing digital information, including,for example, a Dynamic Random Access Memory (DRAM) integrated circuitdie, a Static Random Access Memory (SRAM) integrated circuit die, aSynchronous Graphics Random Access Memory (SGRAM) integrated circuitdie, a Programmable Read-Only Memory (PROM) integrated circuit die, anElectrically Erasable PROM (EEPROM) integrated circuit die, a flashmemory die and a microprocessor die, and that the present inventionincludes such devices within its scope. In addition, it will beunderstood that the shape, size, and configuration of bond pads, jumperpads, dice, and lead frames may be varied without departing from thescope of the invention and appended claims. For example, the jumper padsmay be round, oblong, hemispherical or variously shaped and sized solong as the jumper pads provide enough surface area to accept attachmentof one or more wire bonds thereto. In addition, the bond pads may bepositioned at any location on the active surface of the die.

As shown in drawing FIG. 10, an electronic system 130 includes an inputdevice 132 and an output device 134 coupled to a processor device 136,which in turn, is coupled to a memory device 138 incorporating theexemplary semiconductor device 24 and T-interposer 26 of drawing FIG. 2.

Accordingly, the claims appended hereto are written to encompass allsemiconductor devices including those mentioned. Those skilled in theart will also appreciate that various combinations and obviousmodifications of the preferred embodiments may be made without departingfrom the spirit of this invention and the scope of the accompanyingclaims.

1. A conductive apparatus interposed between a first semiconductordevice and a second semiconductor device, the first semiconductor deviceand the second semiconductor device each having a plurality of bond padson an active surface thereof and a bottom surface, the conductiveapparatus comprising: a substrate having a coefficient of thermalexpansion essentially matching or similar to each of the firstsemiconductor device and the second semiconductor device; a firstsurface having a first length and a first width; and a second surfacehaving a length and a width smaller than the first width of the firstsurface, the first surface comprising an overhang portion of theconductive apparatus that protects the plurality of bond pads disposedon the first semiconductor device and the second surface being mountableto the active surface of the first semiconductor device.
 2. Theconductive apparatus according to claim 1, wherein the overhang portionfurther comprises at least one conductive strip for connection to atleast one bond pad of the plurality of bond pads of the firstsemiconductor device.
 3. The conductive apparatus according to claim 1,wherein the first and second surfaces are formed from a common unitarymember.
 4. The conductive apparatus according to claim 1, wherein theconductive apparatus provides thermal conductivity for thermal energytransfer from the first semiconductor device and the secondsemiconductor device, each mounted to the conductive apparatus.
 5. Theconductive apparatus according to claim 1, wherein the conductiveapparatus provides electrical insulation between the first semiconductordevice and the second semiconductor device, each mounted to theconductive apparatus.
 6. The conductive apparatus according to claim 1,wherein the conductive apparatus provides one of thermal conductivityand thermal insulation between the first semiconductor device and thesecond semiconductor device, each mounted to the conductive apparatus.7. The conductive apparatus according to claim 1, wherein the conductiveapparatus provides electrical insulation between the first semiconductordevice and the second semiconductor device, each mounted to theconductive apparatus.
 8. The conductive apparatus according to claim 1,wherein the conductive apparatus provides thermal conductivity andelectrical insulation between the first semiconductor device and thesecond semiconductor device, each mounted to the conductive apparatus.9. The conductive apparatus according to claim 1, wherein the conductiveapparatus provides thermal insulation and electrical insulation betweenthe first semiconductor device and the second semiconductor device, eachmounted to the conductive apparatus.
 10. The conductive apparatusaccording to claim 3, wherein the common unitary member has acoefficient of thermal expansion substantially equal to that of thefirst semiconductor device.
 11. The conductive apparatus according toclaim 3, wherein the common unitary member has a coefficient of thermalexpansion substantially equal to that of the second semiconductordevice.
 12. The conductive apparatus according to claim 3, wherein thecommon unitary member has a coefficient of thermal expansionsubstantially equal to that of the first semiconductor device and thesecond semiconductor device.
 13. The conductive apparatus according toclaim 1, wherein the first surface of the conductive apparatus isconnected to a base portion of the second semiconductor device.
 14. Theconductive apparatus according to claim 13, wherein a thirdsemiconductor device is mounted adjacent the second semiconductordevice.
 15. The conductive apparatus according to claim 1, wherein thelength of the second surface is substantially the same as the firstlength of the first surface.
 16. The conductive apparatus according toclaim 1, wherein the length of the second surface is substantially thesame as the width of the second surface.
 17. A conductive apparatus forinterposing between a plurality of semiconductor devices, eachsemiconductor device of the plurality of semiconductor devices having atleast one bond pad on an active surface thereof and a bottom surface,comprising: a first surface having a first length and a first width; asecond surface having a length and a width smaller than the first widthof the first surface, the first surface providing a protective overhangportion over the at least one bond pad on an active surface of a firstsemiconductor device of the plurality of semiconductor devices and thesecond surface being mountable to the active surface of the firstsemiconductor device.
 18. The conductive apparatus according to claim17, further comprising: a third surface having a first length and afirst width; a fourth surface having a length and a width smaller thanthe first width of the third surface, the third surface providing aprotective overhang portion that protects the at least one bond pad onan active surface of a second semiconductor device of the plurality ofsemiconductor devices and the fourth surface being mountable to theactive surface of the second semiconductor device.
 19. The conductiveapparatus according to claim 17, wherein the protective overhang portionfurther comprises at least one conductive strip for connecting to thefirst semiconductor device.
 20. The conductive apparatus according toclaim 17, wherein the first and second surfaces are formed from aunitary member.
 21. The conductive apparatus according to claim 18,wherein the third and fourth surfaces are formed from a unitary member.22. The conductive apparatus according to claim 17, wherein theconductive apparatus provides thermal conductivity, thermal insulation,and electrical insulation between the first semiconductor device and asecond semiconductor device of the plurality of semiconductor devicesconnected to the conductive apparatus.
 23. The conductive apparatusaccording to claim 20, wherein the unitary member has a coefficient ofthermal expansion substantially the same as the first semiconductordevice.
 24. The conductive apparatus according to claim 21, wherein theunitary member has a coefficient of thermal expansion substantially thesame as the first semiconductor device.
 25. The conductive apparatusaccording to claim 17, wherein the first surface of the conductiveapparatus is connected to a base portion of a second semiconductordevice of the plurality of semiconductor devices.
 26. The conductiveapparatus according to claim 25, wherein at least a third semiconductordevice is mounted adjacent the second semiconductor device of theplurality of semiconductor devices.
 27. The conductive apparatusaccording to claim 17, wherein the length of the second surface issubstantially the same as the first length of the first surface.
 28. Theconductive apparatus according to claim 17, wherein the length of thesecond surface is substantially the same as the width of the secondsurface.